> Documentation examples are meant to be read, not executed

I agree, but several of them already run, and others run with the addition of doctests directives (that are hidden in the html output).  If the code needs to be changed in a way that is less readable, the test can just be skipped.

> Furthermore, spreading unit tests in the doc files instead of Lib/test
> files will make maintenance of tests more tedious as well.

Tests should be kept in Lib/test, this is mostly to make sure that the examples are correct.  The examples in the docs should still be written with the goal to be clear for the user -- being valid doctests is a secondary goal.